A Comparison of Boundary Layer Parameterizations and Sensitivity to Vertical Resolution with the 3-km FV3 Stand-Alone Regional Model for a Lake-Effect Snow Event

With the transition from the spectral GFS to the non-hydrostatic FV3, various tests on the performance of the FV3 model with different physics configurations and vertical resolution becomes imperative. As such, testing the compatibility of physics with different vertical level spacing, particularly within the planetary boundary layer (PBL), will allow a deeper understanding of what deficiencies exist for different fine-scale phenomena, and to, where possible, make improvements in both physics and vertical resolution. An effective way to evaluate the impact of these changes is to evaluate sensitivity tests with a set of configurations and compare the results with available data sources.

In this study a notable lake effect snow event from 12/25/2017 is evaluated for sensitivities to PBL parameterization and vertical resolution. Two candidate PBL schemes for evaluation include the hybrid Eddy Diffusivity Mass Flux (HYB-EDMF) scheme, which relies on Prandtl number relationships and a height varying eddy-diffusivity profile—calculated differently based on PBL regime—to determine eddy diffusivity. The second scheme is the Scale Aware-TKE EDMF (SAT-EDMF), which uses the Turbulent Kinetic Energy explicitly to calculate eddy diffusivity. The SAT-EDMF PBL also enhances buoyancy as a result of including the process of condensation inside the heat flux term. The vertical resolutions tested in conjunction with the different PBL configurations include those based off current operational systems (e.g. GFS and NAM). Sources of data to be used for evaluation include Multi-Range Multi-Sensor (MRMS) radar reflectivity and snow analysis from the National Operational Hydrologic Remote Sensing Center’s National Snowfall Analysis.